In general, turbines, in particular steam turbines, for converting thermal energy in mechanical work are typically used in thermal power stations. The thermal power stations produce thermal energy by combustion of fossil material, by the use of nuclear reactors or by solar power, for instance. In conventional thermal power stations thermal energy may be produced 24 hours a day, so that the power generating turbines need not to be shut down under regular conditions.
A turbine that is cooled down and in a power off state requires a long start-up phase until the regular operating conditions of the turbine are reached. For instance, the rotation speed of the rotor blades in the turbine has to be accelerated slowly, so that disadvantageous operating conditions, such as the surge of the turbine, do not occur. Surging is defined as a self oscillation of the discharge and flow rate pressure of the turbine, including a flow reversal.
In modern times, it is an aim to produce more and more renewable energy from ecologically friendly energy sources. One exemplary power station that produces energy from an ecologically friendly energy source is the solar power station. In solar power stations electricity is generated by means of sunlight. A typical solar-thermal power station comprises solar collectors, such as parabolic reflectors, in order to concentrate sunlight to a small surface for generating heat. With the thermal energy generated by the sunlight a working medium for a turbine is heated up. The working medium may be a fluid, such as suitable oil materials or water, in a vapour or steam state. The heated steam is guided through the turbine that converts the thermal energy in mechanical work, wherein a subsequent generator converts the mechanical work in electricity.
Solar-thermal power stations only operate during day time when the sun is shining. During night time, the solar-thermal power stations are shut off and thus the turbines as well. During the night time, the turbines are cooling down to the ambient air temperature. At the next day, when the turbine is started again, a long start-up phase is necessary until the turbine reaches the operating temperature and thus an adequate efficiency.
The start-up phase of conventional turbines for solar power stations may endure up to 1 to 1.5 hours until the turbines reaching its operational state. Thus, the overall working time of the turbines during day time may be reduced by 1 to 1.5 hours which leads to a lack of productivity and efficiency of the overall solar power station.